Major League Baseball’s investigation into Alex Rodriguez and other players is being built on testimony and evidence provided by many witnesses in addition to the cooperation of the anti-aging clinic’s founder, Anthony Bosch, a source familiar with the probe said Thursday … According to the source, interviews with “tons” of people will help frame the basis of MLB’s investigation.

This could mean something. It could mean nothing. It totally depends on who those witnesses are.

For example, if the “tons” of witnesses are merely other Biogenesis employees, you have the same problems that Major League Baseball has with Anthony Bosch. Many of these employees are alleged to have tried to sell their story to the media and to sell records and documents as well. Moreover, they all may, like Bosch in most cases, be a step removed from the players themselves, having sold drugs to intermediareis, employees of players and people like that. As we learned the other day, arbitrators will want to have direct evidence of player use of drugs, not just delivery or purchase.

More damning witnesses, however, would be the “intermediaries” mentioned in Tuesday’s ESPN report. The people who actually supplied drugs to players. For example, if MLB has access to that employee of the Levinson Brothers who is alleged to have given drugs to players and attempted to cover up their use, that would be pretty darn significant. Or people who witnessed players actually taking banned drugs. The simple notion, though, that the sheer number of witnesses equals a strong case is wrong. After all, the Clemens prosecutors called 23 witnesses. That didn’t work out so good.

So yes, this could be pretty big. It just really hinges, however, on who these guys are.

Paxton, 30, has been among the game’s better starters over the past few years. In 2018, he went 11-6 with a 3.76 ERA and a 208/42 K/BB ratio in 160 1/3 innings. The lefty has two more years of arbitration eligibility remaining after earning $4.9 million this past season.

Sheffield, 22, is the headliner in the Mariners’ return. He made his major league debut in September for the Yankees, pitching 2 2/3 innings across three appearances. Two of those appearances were scoreless; in the third, he gave up a three-run home run to J.D. Martinez, certainly not an uncommon result among pitchers. MLB Pipeline rates Sheffield as the Yankees’ No. 1 prospect and No. 31 overall in baseball.

Thompson-Williams, 23, was selected by the Yankees in the fifth round of the 2016 draft. This past season, between Single-A Charleston and High-A Tampa, he hit .299/.363/.546 with 22 home runs, 74 RBI, 63 runs scored, and 20 stolen bases in 415 plate appearances. He was not among the Yankees’ top-30 prospects, per MLB Pipeline.

Swanson, 25, was selected by the Yankees in the eighth round of the 2014 draft. He spent most of his 2018 campaign between Double-A Trenton and Triple-A Scranton/Wilkes-Barre. Overall, he posted a 2.66 ERA with a 139/29 K/BB ratio in 121 2/3 innings. MLB Pipeline rated him No. 22 in the Yankees’ system.

This trade comes as no surprise as the Yankees clearly wanted to upgrade the starting rotation and the Mariners seemed motivated to trade Paxton this offseason. To the Mariners’ credit, they got a good return for Paxton, as Sheffield likely becomes the organization’s No. 1 prospect. The only worry about this trade for the Yankees is how Paxton will fare in the more hitter-friendly confines of Yankee Stadium compared to the spacious Safeco Field. The Yankees are likely not done adding, however. Expect even more new faces before the start of spring training.